Ozone, which causes photochemical smog, is produced by a photochemical reaction of HC and NOx contained in exhaust gas from automobiles and factories. Therefore, reducing the amount of HC and NOx emissions from automobiles is an efficient way to suppress the production of ozone and prevent the occurrence of photochemical smog. Also, purifying ozone in air directly can be one of the ways to prevent the occurrence of photochemical smog. The occurrence of photochemical smog can be prevented more effectively not only by reducing the amount of emissions of reactants such as HC and NOx, but also by purifying a product such as ozone. Thus, an automobile provided with a vehicular air cleaner capable of directly purifying ozone in air has been put into practical use in some places including California in the United States of America. Such a vehicular air cleaner is particularly called as a DOR (Direct Ozone Reduction) system.
For example, Patent Literature 1 discloses a DOR system in which a vehicle component part such as a condenser of an air conditioner carries a metal oxide such as manganese dioxide. The condenser of the air conditioner is disposed at such a position as to be exposed to air during travel of a vehicle, and the manganese dioxide has a function of converting ozone contained in the air into other elements such as oxygen to purify the ozone. Thus, according to the DOR system disclosed in Patent Literature 1, ozone in air can be directly purified while the vehicle is moving.